Static information storage and retrieval – Format or disposition of elements
Reexamination Certificate
1999-06-24
2001-03-27
Nguyen, Viet Q. (Department: 2818)
Static information storage and retrieval
Format or disposition of elements
C365S063000, C257S390000, C257S693000, C257S684000, C257S734000, C257S777000, C257S782000, C257S780000, C257S786000, C257S784000
Reexamination Certificate
active
06208546
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a memory module comprising a plurality of memory chips and capable of being mounted on a various memory board, mother board, etc.
2. Description of the Related Art
Computer programs are increasing larger. In order to process such programs at a high speed, there requires to install a large memory capacity inside a computer. There is provided inside a computer a memory board such as a SIMM (Single In-line Memory Module), DIMM (Dual In-line Memory Module), etc. There are mounted a large number of memory ICs on a memory board. Commonly used memory ICs are memory chips (bare memory chips) scribed from a semiconductor wafer and packaged.
Unfortunately, packaging a memory chip reduces the number of chips mountable on a memory board because memory chips are much larger in dimension than bare chips. As a result, it was necessary to mount memory ICs on both sides of a memory board or to stack a plurality of memory ICs
101
as shown in
FIG. 22
in order to increase the number of memory chips to be mounted. However, mounting memory ICs on both sides of a memory board is unable to further increase the memory capacity because a packaged memory IC is far larger than the size of a memory chip included therein. Also, stacking memory ICs
101
as shown in
FIG. 22
is complex in construction and thus not easy to mount memory ICs. In other words, such memory boards including a plurality of stacked memory ICs are not easy to make in large quantity.
SUMMARY OF THE INVENTION
In order to overcome the abovementioned problems, an object of the present invention is to provide a memory module that is easily mountable on a memory board or mother board and is easy to increase the memory capacity.
A memory module of the present invention comprises a plurality of memory chips scribed from a semiconductor wafer and mounted on a module board and the module board is provided with external connection terminals that are accessible to each memory chip from outside the memory module. Mounting the bare memory chips on the module board helps to reduce the outer dimension of the module board. Also, unlike the case of mounting each memory chip on a memory board, the memory module carrying a plurality of memory chips is easier to mount on a memory board or the like because memory module can be mounted as a unit. Additionally, each memory module can easily be high density and large memory capacity because a plurality of memory modules are contained as a set.
Preferably, mounting 4 memory chips in 2 rows and 2 columns with the longer sides of adjacent rectangular memory chips opposed to each other on the abovementioned module board provides a module board having 4 times of the memory capacity of a memory chip, thereby substantially reducing the outer dimension of the module board. Regularly disposing memory chips on a module board in the above manner significantly reduces wasted mounting space and increases mounting density.
Also, the memory module according to the present invention features the module board formed with a plurality of pads in at least one row. The memory chips are mounted on both sides of the row of pads, concentrating the pads between the memory chips. This particular construction reduces the space for the pads as compared with disposing such pads separately at both sides of each memory chip. It is preferable that a row of pads are formed along the longer side of a memory chip and memory chips are disposed on both sides of the row of pads with connection pads of the memory chips in parallel with the row of the pads on the module board, thereby making the distance between the pads on the module board and the memory chips substantially constant which are effective for connection using bonding wires.
Preferably the memory module of the present invention features the module board formed with a plurality of pads in two rows so that memory chips are disposed at both sides of the rows of pads. Each memory chip is connected by bonding wires to the more distant row of pads rather than the closer row of pads, thereby providing a space necessary to connect the pads on the module board and the memory chip even if the memory chip is disposed adjacent to the pads due to high density mounting. As a result, wire bonding can be carried out easily.
In case of connecting by the abovementioned wire bonding, it is preferable to lead bonding wires alternately from both sides of the row of pads for ease of wire bonding operation in high density.
Alternatively, interconnection between the memory chips and the module board may be established by jointing the pads on the module board and the memory chips by using electrically conductive material such as solder balls or gold balls instead of bonding wires. Such flip chip technology is particularly suitable for high density mounting because the mounting area is substantially the same as the chip size.
It is also preferable that the memory module of the present invention uses 2 or more memory chips scribed from a semiconductor wafer as a unit to be mounted on a module board, thereby requiring less mounting area than mounting separately scribed memory chips and simplifying the alignment of the memory chip on the module board. Also, reducing the component count simplifies the assembling operation. In particular, there are two possibilities of scribing 2 or more memory chips along the longer side or along the shorter side. Also, there are 2 ways of interconnecting the intercoupled or continuous memory chips with the module board by utilizing the abovementioned bonding wires or by the flip chip technique. In any event, it is appreciated that the assembling operation including alignment of the memory chips on the module board can be simplified as compared to assembling a plurality of separate memory chips.
The memory module of the present invention preferably uses a module board formed with a plurality of recesses in the direction of thickness and the recesses and their peripheral areas are formed with electrically conductive material to define a memory chip mounting surface. The recesses may be utilized as external connection terminals, thereby eliminating the need for forming separate lead wires and enabling to mount in the size of the memory module.
Other than utilizing the recesses on the side surface of the abovementioned memory module board as external connection terminals, it is possible to form external connection terminals on the surface of the module board opposite to the memory chip mounting surface. Forming the external connection terminals on the surface of the module board is effective to mount the memory module of the present invention on a separate board in order to mount in the size of the memory module.
By choosing address terminals which are a part of the external connection terminals of the abovementioned module board to the same number as the address terminals of the memory chip, the total number of the external connection terminals can be reduced. In other words, by assigning common addresses to be used to access to each of the memory chips in the memory module, common address terminals can be used for the memory chips, thereby reducing the number of required terminals. Similarly, various control terminals which are a part of the external connection terminals on the module board can be shared with the memory chips, thereby reducing the total number of external connection terminals.
REFERENCES:
patent: 5309011 (1994-05-01), Tazunoki et al.
patent: 5691570 (1997-11-01), Kozuka et al.
patent: 5817530 (1998-10-01), Ball
Dellett and Walters
Nguyen Viet Q.
Niigata Seimitsu Co., Ltd.
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